In this paper, we remove, for semiglobal output feedback control of uncerta
in nonlinear systems, a previous requirement that the high-frequency-gain s
ign be known a priori. Our proposed control scheme is also of the high-gain
observer-type, but it involves a switching between two forms of control, T
he underlying idea is that with the help of the high-gain observer, the hig
h-frequency-gain sign can be identified on-line, provided the designed cont
rol satisfies some domination condition.