AbstractInformation on space‐charge behavior in thick insulated samples aids in understanding the dc characteristics of polymer‐insulated dc cables. The pulsed electroacoustic method is used to investigate several space charge formation factors in 2 mm‐thick polyethylene (PE). The following results were obtained.For measurement factors:(1) A polymeric semiconducting electrode provides a more accurate measurement than does a metal electrode as a result of better matching of acoustic impedance with PE.(2) Within a dc electrical stress range of several tens kV/mm, the space charge distributions under and after dc voltage application are almost the same; this is due to a comparatively long time of space‐charge decay.(3) The space‐charge distribution of a plate sample agrees with that of a cable sample having the same insulation thickness.For insulating material factors:(1) The amount of space charge in crosslinked polyethylene (XLPE) is much larger than that in low‐density PE (base of XLPE).The space charge of XLPE continues to increase even after dc voltage application (24 h); that of LDPE reaches equilibrium with a few hours.(2) The aforementioned space charge difference between XLPE and LDPE is assumed to be caused by ionic impurities in XLPE, not by the additives themselves (acetophenon and cumylalcohol as byproducts of cross linking and a