In wafer fabrication (fab), stacking faults (SF) & crystalline defects in the silicon substrate will affect the yield. Wright Etch is the most common chemical etching method used to delineate SF on both (100) & (111) silicon surface. However, when Wright Etch is used directly, no SF could be revealed, even if the fab wafers are etched up to 40 mins. The reason is that the fab wafers have thin films deposited on it. After delayering by using dry & wet etches and subsequently Wright Etch, the SF were revealed. But this method is tedious & time consuming as it requires a long time to delayer. Thus in this paper the possibility of using HF (aq) to deprocess fab wafer prior to Wright Etch is investigated. A new chemical etching method - 155 Wright Etch has been proposed. This method has been applied to failure analysis for two years in our FA labs. The analytical results show that it is a rapid & reliable method and is effective in the delineation of SF or crystalline defects on fab silicon wafers due to high temperature oxidation, junction spiking, silicon precipitation, contamination, charging damage, BVGO failure and contact chain failure during fab processes.