A structure for testing relative to an MOS transistor, can be easily constructed as part of the CMOS process flow. A doped device well is formed, for example, in a silicon-on-insulator structure. The concentration level in the well corresponds to that for a well of the transistor. Gate insulator and polysilicon layers are formed, and the polysilicon is implanted with dopant, to a concentration level expected in the transistor gate. After gate patterning, the methodology involves forming sidewall spacers and implanting dopant into the active device well, to form regions in the test structure corresponding to the transistor source and drain. Although the concentrations mimic those in the transistor source and drain, these test structure regions are doped with opposite type dopant material. The test structure enables accurate measurement of the gate-body current, for modeling floating body effects and/or for measurement of gate length.