N-type SiC epitaxial layers have been grown in a cold wall CVD reactor using phosphine as the precursor. The phosphorous doping dependencies on phosphine flow rate; growth temperature and C/Si ratio are investigated. Thermodynamic simulations for analysis of the gas phase composition under growth conditions were performed to help understand the phosphorous incorporation mechanism. It is shown that the doping concentration dependence on the phosphine flow rate follows the theoretical prediction when the flow of phosphine is high. However, doping increases faster than expected when the phosphine flow rate is low. The study on the effect of growth temperature showed that phosphorous doping decreased when the temperature is increased from 1500 to 1620degreesC, which is explained by the enhanced desorption of phosphorous-containing species on the growth surface at higher temperature. It was also observed that phosphorous doping is insensitive to the C/Si ratio when C/Si is higher than 3 or lower than 0.8. The phosphorous incorporation increases with decreased C/Si ratio when the C/Si ratio is between 0.8 and 3. This result suggests that phosphorous is incorporated on C site rather than on Si.