In this thesis, monolithic microwave integrated circuits(MMICs) are presented for millimeter-wave and submillimeter-wave or terahertz(THz) applications. Millimeter-wave power generation from solid state devices is not only crucial for the emerging high data rate wireless communications but also important for driving THz signal sources. To meet the requirement of high output power, amplifiers based on InP double heterojunction bipolar transistor (DHBT) devices from the III-V Lab in Marcoussic, F rance are designed for the power generation at millimeter-wave frequency range. For future THz heterodyne receivers with requirements of room temperature operation, low system complexity, and high sensitivity, monolithic integrated Schottky diode technology is chosen for the implementation of submillimeterwave components. The corresponding subharmonic mixer and multiplier for a THz radiometer system are designed based on the monolithic membrane supported Schottky diodes, which is under development at Chalmers University of Technology, Sweden. To simplify the baseband circuitry, the received IF signal from the subharmonic mixer is further amplified and downconverted to the DC range with a low noise amplifier and an active mixer by using GaAs pseudomorphic high electron mobility transistor (pHEMT) technology available from OMMIC, France.