As demand in developed economies stagnates, a handful of component suppliers, including Qualcomm Inc and Synaptics Inc, have left competitors in their wake by expanding in China, where sales of cheap phones made by home-grown companies eclipse pricier models made by Samsung Electronics Co Ltd and Apple Inc.

Increased exposure to China has diluted chipmakers' gross profit margins to somewhere in the mid-40 percent range from an average of nearer 50 percent in developed markets, analysts estimate. The rewards lie in the huge volumes demanded by Chinese handset makers.

"The guys that have traditionally been focused on the developed markets are now starting to see a slowdown," said Stewart Stecker, research analyst at asset management firm AlphaOne Capital Partners.

"The guys that are most focused on emerging markets are seeing healthy growth rates."

Brisk demand for low-priced Android devices in China was the main driver of a 39 percent jump in global smartphone shipments during the quarter ended September 30, according to data published by market research firm IDC.

IDC forecasts that annual smartphone shipments in China, already an $80 billion market, will rise in value to $120 billion by 2017. That's 460 million handsets in need of chips, filters and other components.

A new wave of Asian smartphone makers has emerged to help meet this demand for low-end handsets; companies such as Lenovo Group Ltd, ZTE Corp and Xiaomi Tech - the rising star of cheap, made-in-China smartphones.

"We end up selling more lower-end components into China, which tend in general to be a little lower-margin," said Rick Bergman, chief executive of Synaptics, a San Jose, California-based supplier of touchscreen chips.

In its financial year ended June 29, Synaptics reported a 10 percent rise in revenue from China, a market that accounted for about 60 percent of the company's revenue in the period.

None of the companies mentioned in this article provided data about their margins in China relative to the United States and other regions.

Jeffrey Schreiner, analyst at brokerage Feltl & Co, estimated Synaptics' long-term gross margins in a range of 46 percent to 48 percent as its sales to China grow, compared with 48 percent to 50 percent in developed markets.

"The trade-off is that you're going to chase the growing part of the market with high volumes," he said.

Shares of Synaptics, which also supplies chips to Taiwanese smartphone maker HTC Corp's One model and Sony Corp's water-resistant Xperia - both of which are popular with Chinese consumers - have risen about 60 percent this year.

Its shares have outperformed those of competitors such as Audience Inc, Atmel Corp and Maxim Integrated Products Inc - each of which has been stung by inventory reductions at Samsung, their No. 1 customer, and are only now beginning to move into China in a big way.

CHINA REVENUES

San Diego-based Qualcomm accounts for nearly half of global sales of the "baseband" chips that connect mobile phones to cellular networks. The company derived nearly half its revenue from China in fiscal 2013 ending September 30, up from 32 percent in 2011.

Qualcomm declined to comment for this article.

The company's stock, up 17 percent this year, trades at 14.3 times forward earnings - a discount to the sector average of 29.3, suggesting that its potential has yet to be priced in.

"The trends we are seeing in China are just getting started," said AlphaOne Capital's Stecker, whose company owns shares in RF Micro Devices Inc and Avago Technologies Ltd.

Avago, which makes radio-frequency filters that extend battery life and enable smartphones to work across multiple frequencies, relied on China for 41 percent of its revenue last year, up from 30 percent in 2011.

Its stock, up 41 percent this year, is worth 22 percent more than its close on Friday at $44.61, according to Thomson Reuters StarMine's intrinsic valuation model, a calculation of where a stock should trade based on its most likely growth trajectory over the next decade or more.

Cracking the Chinese market is not easy for U.S. component makers, which are up against the local knowledge and 24-hour support teams of Asian chipmakers.

The most successful to date have been able to emulate Asian rivals - companies such as Taiwan's MediaTek Inc, which provides design assistance to niche smartphone makers that lack the capital and expertise to design their own phones.

Cypress Semiconductor Corp, a San Francisco-based company, has developed cheaper touch sensors for low-end Chinese smartphones that reduce the overall price of the phone, Executive Vice-President Hassane El-Khoury told Reuters.

Cypress relied on its China business for 43 percent of its revenue last year, compared with 39 percent two years earlier.

In the case of Qualcomm, Asian smartphone makers pay lower royalties for the company's network technology and shun its top-tier offerings in favor of cheaper components, all of which eats into profitability.

"Component suppliers have to be willing to accept lower prices, and the phones may have less functionality, so they may have older generations of chips," said Josh Spencer, portfolio manager for the T. Rowe Price Global Technology fund.

The fund, however, likes Qualcomm enough to invest. It also owns shares in Avago, Cypress and Synaptics - which offers its touchscreen chips to Asian buyers at lower prices to match regional competitors.

CATCHING UP

There is still hope for those chipmakers that missed the first boat to China, analysts said, as the market is big enough to prop up sales for latecomers.

"The penetration of smartphones is very low," said Jay Srivatsa, analyst at Chardan Capital Markets. "As that market continues to mature, you are going to see more and more handsets being sold."

In addition to their swelling domestic market, Chinese phone makers are shipping affordable phones to emerging economies elsewhere in Asia and Latin America - all of which makes them lucrative customers for U.S. component suppliers.

"In markets such as China and Latin America, demand for feature phones fell significantly (in the third quarter) as users rushed to replace their old models with smartphones," said Anshul Gupta, principal analyst at market research firm Gartner.

Audience's non-Samsung revenue - mainly revenue from China - will account for 20 to 25 percent of its total revenue in the fourth quarter, Chief Executive Peter Santos told Reuters. It was 12 percent in the second quarter.

As it catches up with competitors with a larger presence in China, Audience, which makes chips that filter out background noise, is beginning now to win business from Xiaomi Tech and ZTE, as well as Huawei Technologies Co Ltd and Lenovo.

"The sheer size of the market makes (China) attractive," said Brian Colello, analyst at Morningstar, who estimated gross margins of around 40 percent for chipmakers selling into China.

"It's lower margin, but volume growth makes up for it."

(Additional reporting by Aurindom Mukherjee, Soham Chatterjee in Bangalore, Clare Jim in Taipei and Miyoung Kim in Seoul; Editing by Robin Paxton)

By Sayantani Ghosh and Neha Alawadhi