Microboiling events associated with the fast transient heating of a micrometer-scale metallic thin film heater immersed in water have been studied. The effect of surface properties on the microboiling transients was examined by modifying the heater surfaces with hydrophobic and hydrophilic alkanethiol self-assembled monolayers (SAMs). The microheaters are thin films of platinum or gold-plated platinum that are approximately tens of micrometers in width and hundreds of micrometers in length. The microheaters are immersed in water and rapidly heated with short (< 10 mus) square voltage pulses. The temperature-time transients of the microheaters are obtained by measuring the heater resistance during the application of the heating pulse. The bubble nucleation event associated with boiling is signaled in the temperature-time transient by an inflection point that results from a change in heat transfer when a vapor bubble forms on the heater. Because of the extremely high heating rates (> 10(8) K/s), superheating occurs and nucleation temperatures as high as 296 degreesC have been measured in water. The surfaces of the gold-plated heaters were coated with a series of hydrophilic [HO(CH2)(6)SH, HO(CH2)(11)SH, and HO(CH2)(16)SH] and hydrophobic [CH3(CH2)(7)SH, CH3(CH2)(11)SH, and CH3(CH2)(15)SH] SAMs. Dramatic differences are observed in the temperature-time transients of the hydrophilic versus hydrophobic SAM-coated microheaters. Microheaters modified with hydrophobic SAMs exhibit lower boiling nucleation temperatures, more pronounced inflection points, and higher average temperatures during microboiling. These differences can be rationalized by considering simple models of surface wetting and surface vapor bubble formation.