Frequency dependence of the heat capacity of semicrystalline polyethylene was measured using light heating modulated temperature DSC (LMDSC). The quasi-isothermal measurement was carried out in! the melting temperature range of the crystal. Two decades of the frequency, from 0.01 to 1 Hz, was covered by the LMDSC instrument constructed in the author's laboratory. It was found that in the melting temperature range polyethylene exhibited Debye relaxation with the relaxation time of 14 s and had excess heat capacity independent of the kinetics. The excess heat capacity and the relaxation strength could be attributed to the disordered crystals generated during rapid cooling from the molten state and/or its surrounding amorphous region instead of the stable crystals reorganized during the quasi-isothermal measurement.