  We have developed CMOS imaging sensor (XRPIX) using SOI
(Silicon-On-Insulator) technology for the X-ray astronomical use. XRPIX(X-Ray
soiPIXel) has advantage of a high time resolution, a high position resolution
and an observation in a wide X-ray energy band with a thick depletion layer of
over 200um.
  However, the energy resolution of XRPIX is not as good as one of X-ray CCD.
Therefore improvement of the the energy resolution is one of the most important
development item of XRPIX. In order to evaluate the performance XRPIX more
precisely, we have investigated on the temperature dependence of the basic
performance, such as readout noise, leak current, gain and energy resolution,
using two type of XRPIX, XRPIX1 and XRPIX2b_CZ.
  In our study, we confirmed the readout noise, the leak current noise and the
energy resolution clearly depended on the operating temperature of XRPIX. In
addition, we divided the readout noise into the leak current noise and the
circuit origin noise. As a result, we found that noise of the electronic
circuitry origin was proportional to the square root of operating temperature.
