An experimental study has been performed on single-phase heat transfer, boiling inception, and pressure drop of R-123 over a bank of shrouded micro pin fins 243 mu m long with hydraulic diameter of 99.5 mu m. Heat transfer coefficients and Nusselt numbers have been obtained over effective heat fluxes ranging from 3.5 to 65.5 W/cm(2) and Reynolds numbers from 134 to 314. A delay in boiling incipience has been observed and a meta-stable single-phase region was apparent at liquid exit temperatures noticeably exceeding the saturation temperature. Once boiling was initiated, vapor burst instabilities resembling the compound relaxation instabilities were attained. It has also been found that endwalls effects on heat transfer diminished for Re > 100. (c) 2006 Elsevier Ltd. All rights reserved.