An ultrasmall plasmonic coaxial laser made of metal–semiconductor–metal on a silicon substrate through an interlayer bonding was designed. From the effective refractive indices and the transparent material gain, the nanoscale structural dimensions with both the radius and the width at 80 nm for the coaxial plasmonic waveguide were decided. The influence of the interlayer bonding material on the optimization of resonant wavelength and Q-factor was evaluated. A three-dimensional body-of-revolution finite-difference time-domain method was used to show that a coaxial cavity with a SiO2 interlayer can laze at around 1480-nm wavelength with a net optical threshold power density of about 800 W/cm2 and a subwavelength mode volume of 0.014(λ/2n)3. This nanolaser on silicon platform will benefit those working on nanophotonic integrated circuits.