This letter presents a K-band phase shifter monolithic microwave integrated circuit (MMIC) which is based on electrically tunable composite left- and right-handed metamaterials. This structure utilizes both positive and negative phase shifting metamaterial characteristics to allow for a wide tuning range. This is achieved by varying both the capacitance and inductance of the metamaterial structure. The inductance tuning is realized by an improved active inductor with a self-resonant frequency greater than 20 GHz. The phase shifter is divided into four sections of unit cell metamaterial and is implemented in 0.13 μm radio frequency complementary metal-oxide-semiconductor (RFCMOS) technology. The phase shifter exhibits a continuous phase tuning range of 121° (from -80° to +41°) and 136° (from -120° to + 16°) at 21.5 and 22.5 GHz, respectively. The minimum insertion loss is -10.1 and -10.5 dB at 21.5 and 22.5 GHz, respectively. At 26 GHz, a wide phase shift of greater than 300° is achieved in a compact chip area of 0.28 mm2.