S to P conversions were employed to derive a coherent discontinuity structure beneath Indonesia. Analysis of data recorded by three regional arrays from nine deep earthquakes not only confirmed the results of previous studies on the existence of the mid-mantle discontinuity beneath the Java arc but also revealed its presence north to Kalimantan Island. S to P waves converted at the discontinuity were observed on the stacked diagrams with a negative slowness relative to the P wave and a conversion depth ranging from ~1080 km in the west to ~930 km in the east.