This paper describes an effect of the inversion of silicon single crystal from p-type to n-type by the irradiation of ruby pulsed laser. This effect is a function of the impurity compensation but independent of the oxygen content, the crystal cut and the crystal-growing process. Experimental results show that p-type silicon crystals with phosphorus impurity compensation higher than 7% are susceptible to inversion by pulsed laser irradiation when the amount of impurity compensation increases and the distribution of impurity compensation changes. The concentration profile of phosphorus atoms is given by SIMA technique.