Photothermal ionization spectroscopy (PTIS)measurements were carried out on a high purity and high quality 4H-SiC epitaxial layer at various temperatures. The two step photothermal ionization process is dearly reflected in the temperature dependence of the photoconductivity. The spectrum at the temperature of 25.6 K reveals five well resolved electronic transition lines associated with the shallow nitrogen donor. The ionization energy of the shallow nitrogen donor is concluded to be 60.2 +/- 0.5 meV. Furthermore, PTI magnetospectroscopy measurements were performed to investigate the symmetry properties of these transitions. The results show no linear Zeeman splitting only diamagnetic shift, which is consistent with the fact that the effective mass tensor of 4H-SiC has three different diagonal components.