Japanese specialty chipmaker Rohm Co Ltd said on Tuesday that it will buy all the shares of U.S. sensor-maker Kionix Inc for an undisclosed sum in a bid to chase the growing motion sensor business.

The cash-rich chipmaker, which last year bought the semiconductor operations of Oki Electric Industry Co, hopes buying Kionix will give it an edge in accelerometers -- a type of micro-electro mechanical systems (MEMS) sensor used in devices including digital cameras and cellphones.

Such sensors are used in Apple Inc's iPhone to detect whether a device is being held horizontally or vertically, and in Nintendo's Wii remote, allowing it to detect hand motion.

Rohm spokesman Kohei Nozato declined to disclose the sales numbers and clients of the unlisted Ithaca, a New York-based firm, but said that the acquisition would not have a significant impact on Rohm's capital.

The MEMS sensor market is dominated by Germany's Robert Bosch [ROBG.UL] and Geneva-based STMicroelectronics, but competition has intensified against the likes of U.S. chipmakers Freescale Semiconductor [FSLSM.UL] and ADI Technologies, as well as Japan's Omron Corp and Panasonic Corp.

Rohm, Japan's eighth-biggest chip maker, last year bought Oki's microchip operations for 86 billion yen ($958 million) to bolster its custom chip lineup with system chips used for digital consumer applications.

It aims to close the deal with Kionix by year-end.

 ($1=89.81 Yen)

(Reporting by Mayumi Negishi; Editing by Joseph Radford)