IP protection is of major importance for a semiconductor company and only limited information is made available for device debugging for the product outsourced to a foundry. In order to position ourselves better in the ever competitive semiconductor industry, with the consideration of IP protection, we have to provide the customers with the Si debugging capability and device/chip verification services in foundry. This paper explores the Si debugging methodology and technique in a foundry. Two case studies are presented and discussed. The first case illustrates the isolation of the failure location by InGaAs microscopy, upon which the failure was identified to be caused by a latch-up issue. In the second case, due to confidentiality considerations from the customer, full information could not be provided to the foundry for silicon debugging. The paper illustrates the ability to effectively debug a failure despite being constrained by limited information from the customer.