An effect induced by x-ray irradiation on Boron-doped crystalline Si at room temperature was closely investigated in this paper. Irradiation of X-ray energy of 40, 55 and 70keV has been performed on P-N junction diodes fabricated at Thai Microelectronics Center. Minority carrier life time of the device has been calculated before and after irradiation for comparison. The results show no significant change on the value between exposed and unexposed device. Therefore, any permanent lattice modified or any defects caused by X-ray in the device bulk seem to be unconfirmed in this range of energy. However, from this study, X-ray irradiation still effects on electrical characteristics of the diodes. Current-voltage (I-V) measurement has been carried out to study characteristic variation of the device. Biasing of the device was performed from -10 to 1 V and, after the exposure, the leakage current was obviously decreased by 25% and forward current was dramatically increased by 3 order of magnitude related to increment of X-ray energy.