Using a recently developed gate-sensing and channel- sensing (GSCS) transient analysis method, we have studied the detailed charge-trapping behavior for SONOS-type devices. By adding gate sensing to the conventional channel sensing, the two variables (total charge Q tot and mean vertical location x circ) can be solved simultaneously. By using this powerful new tool on several SONOS-type structures, we have studied the charge centroid as well as the capture efficiency of various SONOS devices. Our results clearly prove that electrons are mainly distributed inside the bulk nitride instead of the interfaces between oxide and nitride. For the first time, we show that nitride 7 nm or thicker can essentially capture electrons with 100% efficiency up to a density of Q tot ~10 13 cm -2 . Structures without top blocking oxide suffer from hole back tunneling and show apparent low electron capture efficiency, which led to confusion in the past. Moreover, multilayer stacks of nitride-trapping layers do not provide more efficient interfacial traps.