This study aims at finding strategies for avoiding the high contact resistance between gold electrodes and the two-dimensional semiconductor molybdenum disulfide. We demonstrate that tuning the work function (WF) of gold by pyrimidine-containing self-assembled monolayers (SAMs) can be used to eliminate the high injection barrier at the interface between gold electrodes and MoS2. Exfoliated single-crystalline flakes of MoS2 have been used in this study. The flakes were transferred onto pre-fabricated substrates suitable for the fabrication of field effect transistors (FET) comprising SAM-functionalized gold electrodes that act as bottom contacts for MoS2. Through combining the electrical characterization of the MoS2-based FETs with various SAM treated electrodes, and Kelvin probe force microscopy (KPFM) investigations of the devices during operation, the strong influence of the injection barrier on the device performance is revealed. In cases, where the SAMs induce a suitable alignment of the transport levels of the semiconductor flakes with the WF of the electrodes, the contact resistance becomes irrelevant and intrinsic properties of MoS2 become accessible. In contrast, high injection barriers lead to a sizable contact resistance, and almost the entire bias voltage drops at the carrier injection contact. In addition, KPFM was employed to reveal – frequently omitted – asymmetric, non-linear, and bias-dependent components of the contact resistances. As a consequence, the device performance is deteriorated and the drain current drops by over two orders of magnitude