This paper studies the thickness of siliconp‐njunction space‐charge regions at low temperature including the effects of doping‐dependent dielectric permittivity &egr;(N), which is important for heavily doped semiconductor materials because of the presence of unionized impurity atoms that are subjected to polarization. The treatment is applicable forp‐njunctions under all voltages and is not based on the conventional depletion approximation which assumes free carriers are negligible in the space‐charge region. Comparison of the present thickness model including &egr;(N) and the conventional depletion model is included.