Abstract : In order to cater the needs of advanced communication systems, silicon-based RF ICs experience a fast-growing phase. In this work, the design of CMOS oscillator using an SIW (Substrate Integrated Waveguides) based LC-tank circuit is proposed. SIW based LC-tank circuit is preferred in oscillator design to get high performances such as improved phase noise and wide tuning range. In this work, the designed oscillator operates at 4.1 GHz, using the SIW structures that model passive circuit components such as inductors and capacitors. The mentioned components are designed in SIW structures that operate in the range of 2 GHz to 10 GHz. For oscillator design, a balanced differential cross-coupled pairs using NMOS and PMOS transistors are used as the forward amplifier. This design uses 45 nm CMOS technology and results are analyzed in Cadence Virtuoso. The designed SIW components act as feedback elements, which are designed in Ansys HFSS. It is observed that the phase noise of GPDK provided LC-tank is -196.4 dBc at 100 MHz whereas SIW structures based LC-tank show a better phase noise, -246.9 dBc at 100 MHz. The power consumption is 4.976 milliWatts for GPDK provided LC-tank oscillator whereas for SIW based LC-tank is just 1.371 milliWatts at 1 V supply voltage. © 2019 IEEE.