Single electron transistors are formed in an AlGaAs/InGaAs/GaAs modulation-doped heterostructure by Ga focused ion beam implantation. The AlGaAs/InGaAs/GaAs system has a high two-dimensional electron gas density and facilitates a lateral constriction whose depletion length is much smaller than that in a conventional AlGaAs/GaAs system. A dot structure confined by a small depletion spreading of less than 0.15 μm is formed by the ion implantation. This ion implantation is also employed to form in-plane gates for controlling the tunneling junctions between the dot and reservoirs, and the number of electrons in the dot. Coulomb oscillations and a Coulomb staircase have been clearly observed by controlling three in-plane gates.