The spatial wave-function switched field effect transistor (SWSFET) has two or three low band-gap quantum well channels inside the substrate of the semiconductor. Applied voltage at the gate region of the SWSFET, switches the charge carrier concentration in different channels from source to drain region. The switching of electron wave function in different channels can be explained by the device model of the SWSFET. A circuit model of SWSFET is developed in BSIM 4.0.0. The design of three bit analog-to-digital converter (ADC) using one three wells SWSFET is explained in this work. Analog-to-digital converter (ADC) circuit design using less number of SWSFET will reduce the device count in future analog and digital circuit design.