This article investigates the heat transfer performance and stability characteristics of a varying-cross-sectional-area pin fin subject to boiling. Heat transfer performance is evaluated numerically by solving the conduction convection equations, while the corresponding stability is explored via linear stability analysis. Three types of pin fins are considered: truncated conical spines, straight fins, and reversed truncated conical spines. At a fixed base temperature and base area, the base heat transfer rate would follow: truncated conical straight reversed truncated conical spine. The linear stability analysis reveals that for one-mode boiling, transition boiling alone on a fin of all three types of fins would become unstable at a fin length exceeding critical value. A similar result is valid for the film transition boiling mode in multimode boiling. On the basis of the same base area and fin length, the operational region where boiling can carry on smoothly shrinks markedly for a truncated conical spine. However, under the constraint of constant base area and fin volume, contracting fin exhibits a greater range of base superheat to prevent burnout. Experimental investigations are reported to verify the theoretical findings.