Vertical-cavity surface-emitting lasers (VCSELs) have many advantages over edge-emitting devices, but they tend to be more sensitive to increasing current density both in lifetime and reliability. To better understand this relationship, the authors investigated the cause of 35 failures involving GaAs-based oxide-confined VCSELs. This paper presents a summary of the procedures, methods, and equipment used, the defects and damages observed, and the root causes behind each failure. The authors followed a standard failure analysis workflow consisting of PEM and OBIRCH fault isolation, plan view TEM to confirm the location and distribution of defects, and cross-sectional TEM (XTEM) to determine the profile of a defect at a specific site. All failures examined could be attributed to one of four basic failure mechanisms: burnout due to ESD, dislocations, oxide diffusion, and oxide delamination.