This study analyses the frequency response of a bidirectional series-resonant DC/DC converter (SRC) working in a discontinuous mode (DCM). The converter can reach a voltage conversion ratio higher or lower than one, depending on whether the operation mode is step-up or step-down. The analysis is based on a novel mixed technique using both the state-space average method and the Fourier method to obtain a state-space averaged model of the converter. The study presents the model for the two operation modes. It also presents the frequency response of the output voltage as a function of the input voltage and as a function of the off-time, which is the control parameter of the converter. The results of those transfer functions are compared with measurements in a 2000 W prototype. The model provides enough information to properly control the SRC in DCM.