Systematic surveys of both the near and far noise fields were made for a supersonic (nozzle design Mach number 1.5) cold model jet. The operating conditions selected for this investigation were (a) shock‐free mode at operating pressure ratio (reservoir pressure/ambient pressure), ξ=3.57 and (b) underexpanded mode at ξ=4.74. The experiments were conducted in an anechoic chamber. The purpose of this investigation was to extend the existing understanding of the noise field of a supersonic shock‐free jet at a moderate exit Mach number and the variations in its acoustic behavior when the nozzle was operated at its underexpanded mode, where strong shock waves were present. The main experimental results are presented. It was found that the broad‐band pressure spectra of apparent sources in each of the individual characteristic flow regions were grossly similar. The strongest source for the shock‐free jet was located in the region between the laminar core tip and the supersonic core tip, whereas for the underexpanded jet the strongest source was found near the middle of the flow region containing repetitive shock waves. It is shown that the significant increase in the noise output at the underexpanded mode of operation was primarily due to high‐frequency components.