A turbine blade having an internal cooling system with dual serpentine cooling channels in communication with tip cooling channels is disclosed. In at least one embodiment, the cooling system may include first and second tip cooling channels in communication with the first and second serpentine cooling channels, respectively. The first tip cooling channel may extend from the leading edge to the trailing edge and be formed from a first suction side tip cooling channel and a first pressure side tip cooling channel. The second tip cooling channel may extend from a midchord region toward the trailing edge and may be positioned between the pressure and suction sides such that the second tip cooling channel is positioned generally between the first suction side and pressure side tip cooling channels. The first and second tip cooling channels may exhaust cooling fluids through the trailing edge.