This post is for informational purposes only, please review the manufacturer datasheet and specifications to verify that any recommendations are suitable for your application.
G4IBC20W is an IGBT, also known as IRG4IBC20W, that seems to have been discontinued some time ago. Based on the information in this copy of the old datasheet, DigiKey part number 497-5115-5-ND should a viable option as an alternative. It is produced by STMicroelectronics.
However, please note that it is not necessarily a drop-in replacement, so use your best judgement and look over the specifications.