To provide a plasma CVD device and a semi conductor thin film forming method to effectively prevent particles from being deposited on a counter electrode even when the high-voltage reactive gas is used.

The plasma CVD device to form a thin film on a substrate 2 comprises a reaction vessel 1, a grounding electrode 3 which is provided on an inner lower part of the reaction vessel 1, provided with the substrate 2 and connected to a reference voltage source, a counter electrode 4 which is provided on an inner upper part of the reaction vessel 1, arranged opposite to the substrate 2 and connected to a high frequency voltage source, and a mesh electrode 5 which is arranged between the grounding electrode 3 and the counter electrode 4 so that the distance to the counter electrode 4 is as short as not to generate the plasma, and connected to the reference voltage source.