The viscosity of an epoxy-molding compound (EMC) has been characterized using a parallel-plate viscometer and a specially-developed slit rheometer. In particular, steady-state and dynamic viscosities at low temperatures and shear rates have been determined with a parallel-plate viscometer. Measurements with this instrument indicate that an extended Cox–Merz relation can be used to relate the dynamic viscosity to the steady shear viscosity for the given EMC. For measurements at high shear rates and high temperatures, a special slit rheometer has been built. In this viscometer, the slit is preceded by a disk-shaped reservoir where curing of the specimen takes place. The sample fills the thin reservoir fast and has its temperature raised by heat conduction from the hot wall. Because the reservoir is thin, the specimen quickly reaches the wall temperature with negligible cure and then cures under approximately isothermal conditions. The degree of cure of the sample is measured by quenching the specimen as it is extruded out of the slit and then performing differential-scanning-calorimeter measurements. By combining results from these two viscometers, the viscosity of the EMC has been obtained over the typical processing range of shear rates, temperature and degree of cure encountered during chip encapsulation. The measurement results indicate that the EMC viscosity exhibits a yield-stress behavior at low shear rates and a power-law behavior at high shear rates. The temperature dependence can be described by the WLF (Williams–Landel–Ferry) equation and the degree-of-cure dependence at low cure by an equation proposed by Macosko.