An on-chip electromagnetic bandgap (EBG) structure using a CMOS process is proposed. The proposed structure is the first EBG structure devised to suppress simultaneous switching noise coupling in an on-chip power distribution network (PDN). The on-chip EBG structure utilizes an on-chip inductor and a MOS capacitor to generate a stopband with a range of several GHz in an extremely small size; thus, the EBG structure can be embedded in on-chip PDNs. The proposed on-chip EBG structure was fabricated using a MagnaChip 0.18µm CMOS process, and we successfully verified a 9.24 GHz stopband, from 1.26 to 10.5 GHz, with an isolation level of 50 dB.