Low temperature scanning laser microscopy (LTSLM) is demonstrated to be capable of imaging sub-THz electromagnetic fields in cryoelectronic integrated structures. This method allows one to evaluate the spatial distribution of time-averaged field amplitudes with a resolution of about one micrometer for samples with characteristic dimensions of order millimeters. Using LTSLM, cryoelectronic devices with both passive and active superconducting elements can be characterized. Local heating of superconducting structures by a laser beam introduces extra loss for the propagating and standing sub-millimeter waves. We present LTSLM images of two-dimensional 400 to 500 standing GHz wave patterns in integrated superconducting receiver chips.