P-n junction is the main 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 since the equipment for these methods is expensive. A possibility of p-n junction formation by laser radiation was shown in several p- and n-type semiconductors: p-Si[1,2], p-CdTe[3], p-InSb[4,5], p-InAs[6], p-PbSe[7] and p-Ge[8] due to inversion of conductivity type. Unfortunately, the mechanism of p-n junction formation by laser radiation is not clear until now. In the present research rectification effect of current-voltage characteristic in pure intrinsic Ge crystal after irradiation by Nd:YAG laser was observed. The effect is characterised by threshold intensity of the laser radiation. Increase of rectification ratio of current-voltage characteristics and barrier height with intensity of the laser radiation, energy of laser radiation quanta and number of pulses was 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. [1] Y. Mada et al. Appl. Phys. Lett., 48, pp. 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). Acknowledgments. The author gratefully acknowledges financial support in part by Europe Project in the Framework of MATERA+ project, European Regional Development Fund within the project “Sol-gel and laser technologies for the development of nanostructures and barrier structures”, the ESF Projects No. 1DP/1.1.1.2.0/09/ APIA/VIAA/142 and «Support for the implementation of doctoral studies at Riga Technical University».