We use the two-dimensional (2-D) scattering matrix method (SMM) to analyze the slot characteristics in slotted singlemode semiconductor lasers and compare the results with those calculated by the one-dimensional transfer matrix method (TMM). The analysis shows that the 2-D SMM is required to accurately account for the measured results. Using the 2-D SMM simulation, we find that there is almost no reflection at the interface from slot to waveguide while a large reflection exists at the interface from waveguide to slot, and the power loss is much larger than the power reflected. For a single slot, the slot width has little influence on the slot reflectivity, which coincides with the measured results. The reflection and transmission of the slot are found to be exponentially dependent on the slot depth.Index Terms-Perfectly matched absorption layers (PMLs), scattering matrix method, semiconductor lasers, single-mode laser, transfer matrix method.