P-n junction is the most important component of many semiconductor devices. Thermodiffusion, ion implantation and molecular beam epitaxy are only a few methods to form a p-n junction. The main drawback for these methods is high cost per p-n junction. A possibility of p-n junction formation by laser radiation was shown in several semiconductors: p-Si[1,2], p-CdTe[3], p-InSb[4,5], p-InAs[6], p-PbSe[7] and p-Ge[8]. Different mechanisms have been proposed to explain the nature of inversion of conductivity type: impurities’ segregation, defects’ generation, amorphization and oxygen related donor generation. However, the proposed mechanisms have many lacks and even contradictions; therefore the mechanism of p-n junction formation by laser radiation is not clear until now. For the understanding it, i-Ge crystal was irradiated by Nd:YAG laser with different energy of quantum. The crystal was used in the experiments as a model material because the concentration of impurities in this material is lower than the concentration of intrinsic point defects at RT. Increase of rectification ratio of I-V characteristics and barrier height with intensity of the laser radiation, energy of laser radiation quanta and numbers of pulses were observed in this experiment. The mechanism of this phenomenon is explained by generation and redistribution of intrinsic point defects in temperature gradient field, which causes strongly absorbed laser radiation. The redistribution of defects takes place because interstitial atoms drift towards the irradiated surface, but vacancies drift in the opposite direction – in the bulk of semiconductor according to Thermogradient effect. Since interstitials in Ge crystal are of n-type and vacancies are known to be of p-type, a p-n junction is formed. References 1. Y. Mada et al. Appl. Phys. Lett., 48, 1205 (1986). 2. J. Blums et al. Physics Status Solidi (a), K91, (1995). 3. A. Medvid’ et al., Radiat. Meas., 33, 725 (2001). 4. I. Fujisawa, Jap., J. Appl. Phys, 19, 2137 (1980). 5. A. Medvid‘ et al. Vacuum, 51, 245 (1998). 6. L. Kurbatov et al. Reports of Acad. Sc.USSR, 268, 594 (1983) 7. K.D. Tovstyuk et al. Ukrainian Journal of Physics, 21, 1918 (1984). 8. S.G. Kiyak et al. Physics and Technics of Semiconductors, 18, 1958 (1984).