TAIPEI (Reuters) - Taiwan Semiconductor Manufacturing Co Ltd (TSMC) (>> Taiwan Semiconductor Mfg. Co. Ltd.) on Thursday said revenue is likely to fall in the second quarter from the first, due in part to the loss of business at one of its key customers.

The world's largest contract chip manufacturer expects a decline of 7 percent to 8 percent in April-June. In the three months prior, revenue was flat on quarter but grew 50 percent on year, pushing net profit beyond analyst estimates.

The forecast comes a week after rival Samsung Electronics Co Ltd (>> Samsung Electronics Co Ltd) said it used its own chips in its just-released flagship smartphone instead of chips from Qualcomm Inc (>> QUALCOMM, Inc.), which contracts a large share of its production to TSMC.

"A key customer's business loss to an IDM ... will negatively impact our business," TSMC Chief Financial Officer Lora Ho said in a quarterly analyst conference, without identifying the IDM or the customer.

IDM refers to companies like Samsung which both design and manufacture chips, unlike TSMC which only manufactures them.

The development follows TSMC's presumed loss of orders to Samsung for chips for Apple Inc's (>> Apple Inc.) next iPhone, likely due out this year, analysts said. Estimates for TSMC's share in the handset's next iteration range from 30 percent to 50 percent, from as much as 100 percent in the iPhone 6 models.

At the lower end of the smartphone market, declining prices worldwide may drive handset makers to opt for smaller players such as Semiconductor Manufacturing International Corp (>> Semiconductor Manufacturing Int'l) and United Microelectronics Corp (>> United Microelectronics Corp.) which offer more competitive prices for less-advanced technology, analysts said.

SLOWING MARKET

TSMC said the chip industry - from design to manufacturing and testing - is likely to grow 4 percent this year, rather than 5 percent forecast in January, and that revenue growth in manufacturing alone will be more 10 percent than 12 percent.

"Emerging countries' demand for low-end smartphones is relatively weak" in the short-term, said spokeswoman Elizabeth Sun. "We're also seeing some delay in the launch of high-end phones from Android brands other than Samsung."

TSMC also sliced $1 billion from its capital expenditure plan for 2015, largely attributed to improved efficiency rather than weak demand.

For the three months through March, TSMC said net profit rose 65 percent to T$79 billion ($2.54 billion), beating the T$77.8 billion average estimate of 22 analysts polled by Reuters.

Ahead of the earnings, TSMC shares closed up 2.8 percent versus a 1.2 percent rise in the overall TAIEX <.TWII> index.

($1 = 31.1200 Taiwan dollars)

(This version of the story adds revenue outlook, industry outlook, executive comments)

(Editing by Christopher Cushing)

By Michael Gold