This work has, for the first time, numerically and experimentally proved the existence of metastable regimes in fin boiling process. The linearly stable steady states were subject to external perturbations. As the linearly stable steady state moves toward the critical points on the boiling curve by increasing base temperature, which is linearly unstable in nature, the capability of the steady state to tolerate perturbation becomes weaker. Stable and metastable regimes could be subsequently identified. To operate at metastable boiling regime might induce (nonlinear) instability if the magnitude of external perturbation is large enough. Experimental results support these numerical findings. A proper boiling fin design should take into consideration both the stable and metastable regimes. (C) 2000 Elsevier Science Ltd. All rights reserved.