A method of characterizing semiconductor device includes providing a silicon-on-insulator (SOI) substrate with at least a body-tied (BT) SOI device and a BT dummy device for measurement, respectively measuring tunneling currents (Igb) and scattering parameters (S-parameters) of the BT SOI device and the BT dummy device, subtracting Igb of BT dummy device from that of the BT SOI device to obtain Igb of a floating body (FB) SOI device, filtering characteristics of the BT dummy device out to extract S-parameters of the FB SOI device, and analyzing the S-parameters of the FB SOI device to obtain gate-related capacitances of the FB SOI device.