A side channel compressor for compressing a gas comprises a housing (3), a side channel (30), located in the housing (3) and having a cross-sectional area (A), for compressing a gas, a gas inlet opening (31) formed in the housing (3), the gas inlet opening (31) being in flow connection with the side channel (30) for introducing a gas, a gas outlet opening (32) formed in the housing (3) for discharging the gas to be compressed from the side channel (30), wherein the gas outlet opening (32) is in flow connection with the gas inlet opening (31) via the side channel (30), and an impeller (2) which is mounted for rotation in the housing (3) and comprises impeller blades (1) disposed in the side channel (30), wherein the cross-sectional area (A) of the side channel (30) decreases non-monotonically from the gas inlet opening (31) towards the gas outlet opening (32).