An Ni Schottky contact on the AlGaN/GaN heterostructure is fabricated. The flat-band voltage for the Schottky contact on the AlGaN/GaN heterostructure is obtained from the forward current-voltage characteristics. With the measured capacitance-voltage curve and the flat-band voltage, the polarization charge density in the AlGaN/GaN heterostructure is investigated, and a simple formula for calculating the polarization charge density is obtained and analyzed. With the approach described in this paper, the obtained polarization charge density agrees well with the one calculated by self-consistently solving Schrodinger’s and Poisson’s equations. An Ni Schottky contact on the AlGaN / GaN heterostructure is fabricated. The flat-band voltage for the Schottky contact on the AlGaN / GaN heterostructure is obtained from the forward current-voltage characteristics. With the measured capacitance-voltage curve and the flat-band voltage, the polarization charge density in the AlGaN / GaN heterostructure is investigated, and a simple formula for calculating the polarization charge density is investigated self-consistently solving Schrodinger’s and Poisson’s equations.