In this study, a report is prepared on significantly low specific contact resistivity of alloyed and non-alloyed ohmic contacts fabricated on an as-grown n+-GaN layer and measured with the transfer length method. A low rho c = 8 x 10-8 Omega cm2 is extracted for the alloyed Ti/Al/Ni/Au, and rho c = 4 x 10-7 Omega cm2 for the unannealed Ti/Pd/Au. To achieve these, a highly doped n+-GaN layer with ND = 1.5 x 1019 cm-3 is used. The results are derived from a study of three different metal contact stacks, namely Ti/Al/Ni/Au (20 nm/300 nm/20 nm/400 nm), Ti/Pd/Au (2 nm/5 nm/200 nm), and Mo/Au (30 nm/200 nm). The Ti/Al/Ni/Au metal contact is studied in both annealed and non-annealed conditions, whereas for the Ti/Pd/Au and Mo/Au ohmic contacts, a study is conducted without annealing. Their performance and thermal stability are evaluated with a four-probe TLM, with temperatures ranging from 25 to 150 degrees C. Finally, a theoretical model based on thermionic emission theory is employed to gain a deeper understanding of the physical mechanisms governing the behavior of the ohmic contacts.