This letter designs an LC-tank injection-locked frequency tripler (ILFT) fabricated in 0.18- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> BiCMOS process. The ILFT circuit is made of a differential input and differential output first-harmonic injection-locked oscillator (ILO) and a direct-injection mixer-type frequency tripler (FT) to supply an injection signal to the ILO. As verified by simulation, the ILO uses the inductive peaking technique to increase the ILO locking range and the direct-injection mixer aided by the injection-generated frequency doubler input signal also increases the locking range. The free-running frequency of the ILO is around 4.6 GHz. At the dc power consumption of 9.52 mW and at the incident power of 0 dBm, the output locking range is from the frequency 3.36–5.4 GHz. The whole chip occupies an area of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.1980 \times 1.2$ </tex-math></inline-formula> mm.