We study quantum mechanically self-similar black hole formation by a collap
sing scalar field and find the wave functions that give the correct semicla
ssical limit. In contrast with classical theory, the wave functions for bla
ck hole formation even in the supercritical case have not only incoming flu
x but also outgoing flux. From this result we compute the rate for black ho
le formation. In the subcritical case our result agrees with the semiclassi
cal tunneling rate. Furthermore, Re show how to recover the classical evolu
tion of black hole formation from the wave function by defining the Hamilto
n-Jacobi characteristic function as W=(h) over bar Im ln psi. We find that
the quantum-corrected apparent horizon deviates from the classical value on
ly slightly without any qualitative change even in the critical case.