$\mathrm{In}\mathrm{P}∕\mathrm{Ga}\mathrm{In}\mathrm{As}\mathrm{P}$ square-resonator microlasers with an output waveguide connected to the midpoint of one side of the square are fabricated by standard photolithography and inductively-coupled-plasma etching technique. For a $20\text{-}\mu \mathrm{m}$ -side square microlaser with a $2\text{-}\mu \mathrm{m}$ -wide output waveguide, cw threshold current is $11\mathrm{mA}$ at room temperature, and the highest mode Q factor is $1.0\times {10}^4$ measured from the mode linewidth at the injection current of $10\mathrm{mA}$ . Multimode oscillation is observed with the lasing mode wavelength $1546\mathrm{nm}$ and the side-mode suppression ratio of $20\mathrm{dB}$ at the injection current of $15\mathrm{mA}$ .