In this paper, we present design guideline and simulation results of capacitive micromachined ultrasonic transducer (CMUT) embedded field effect transistor (FET) for high frequency mode operation. The CMUT-FET consists of a mechanical CMUT part and an electrical sensing FET part. The device has a characteristic of a shared gate dielectric between a CMUT and an FET; hence, the gate capacitance change in the CMUT part can be reflected to the FET current as pressure changes. With an FET's current amplifying characteristic, the CMUT-FET makes it possible to achieve higher sensitivity and high resonant frequency with smaller element pitch and smaller active cell area than existing CMUTs. Combination of a 3-D finite element analysis (FEA) model of the CMUT part and a commercial technology computer aided design (TCAD) simulation of the FET device was used for inspection of the CMUT-FET device performance. In the 3-D FEA simulation, we focused on investigating pull-in voltage and electrical potential of a rectangular CMUT plate which have 20MHz resonant frequency in immersion with different dimensions. The FET part simulation was performed with variation of gate oxide thickness, source/drain doping concentration, channel doping concentration, substrate doping concentration. We combined data and inspected overall device performance with pressure variation at specific gate voltage and optimized the factor above-mentioned to get high sensitivity. Simulation results show that the optimized model has the collapse voltage of 13.4V and the pressure sensitivity of 11.34μA/Pa at gate voltage of 11V.