A classical 3-port optical circulator is demonstrated on the silicon-on-insulator (SOI) platform. A garnet die with a magneto-optical cerium-doped yttrium iron garnet (Ce:YIG) layer is bonded on top of a Mach-Zehnder interferometer circuit using a thin adhesive bonding layer. The power transmission between different ports is characterized in the presence of an external magnetic field, transversal to the light propagation direction. An isolation of 22 dB is measured at a wavelength of 1562 nm.