A differential AC chip calorimeter based on commercially available sensors is described. Due to the differential setup pJK－1 sensitivity is achieved. Heat capacity can be measured for sample masses below one nanogram. This corresponds to heat capacities below one nJK^-1 even above room temperature as needed for the study of the glass transition in nanometer thin polymeric films. The calorimeter allows for the frequency dependent measurement of complex heat capacity in the broad frequency range from 1 Hz to 1 kHz for sample masses of some nanograms.