* Q3 revenue seen at $8.12-$8.22 bln range vs $7.06 bln in Q2
* Says to offer guidance in US$ to smoothen currency effect
* Q2 net profit T$66.27 bln vs T$68.44 bln forecast of analysts (Adds Q3 guidance)
TAIPEI, July 13 (Reuters) - Taiwan Semiconductor Manufacturing Co, the world's largest contract chipmaker and a key Apple supplier, forecast third-quarter revenue to rise at least 15 percent from the last quarter due to new mobile devices-related product launches.
Taiwan's most valuable company, which has a market capitalisation that exceeds Intel Corp's, said on Thursday revenue for the July-Sept quarter will be between $8.12 billion and $8.22 billion, compared to the $7.06 billion posted for the April-June quarter.
TSMC and its rivals are riding a boom in demand for chips that power smartphones and computer servers, driving sharp gains in their shares. South Korea's Samsung Electronics Co last week estimated a record quarterly operating profit for April-June.
Apple is gearing up to launch its latest iPhone version, and analysts expect TSMC and some other suppliers to benefit from it.
TSMC's brighter outlook came after its second-quarter net profit fell 8.6 percent from the same period a year ago due to a seasonally weaker quarter and an "unfavorable foreign exchange rate", the company said.
Net profit for April-June was T$66.27 billion ($2.19 billion), down from T$72.51 billion in the year-ago quarter. That compared to the T$68.44 billion average forecast of 22 analysts, according to Thomson Reuters.
TSMC also said it will from this quarter offer revenue guidance in U.S. dollar terms, a departure from denoting it in Taiwan dollars, because of the unfavorable on-year appreciation of the local currency, which it said has been making its revenue appear less than it was.
Revenue in U.S. dollar terms fell 5.9 percent in the second quarter from the previous quarter, but was up 3.2 percent from a year ago, the company said. ($1 = 30.2730 Taiwan dollars) (Reporting by Jess Macy Yu and J.R. Wu; Editing by Muralikumar Anantharaman)