Our understanding of the large-scale population dynamics of neural activity is limited, in part, by our inability to record simultaneously from large regions of the cortex. Here, we validated the use of a large-scale active microelectrode array that simultaneously records 196 multiplexed micro-electrocortigraphical (?ECoG) signals from the cortical surface at a very high density (1,600 electrodes/cm<
sup>
2<
/sup>
). We compared ?ECoG measurements in auditory cortex using a custom ?active? electrode array to those recorded using a conventional ?passive? ?ECoG array. Both of these array responses were also compared with data recorded via intrinsic optical imaging, which is a standard methodology for recording sound-evoked cortical activity. Custom active ?ECoG arrays generated more veridical representations of the tonotopic organization of the auditory cortex than current commercially available passive ?ECoG arrays. Furthermore, the cortical representation could be measured efficiently with the active arrays, requiring as little as 13.5 s of neural data acquisition. Next, we generated spectrotemporal receptive fields from the recorded neural activity on the active ?ECoG array and identified functional organizational principles comparable to those observed using intrinsic metabolic imaging and single-neuron recordings. Furthermore, this new electrode array technology has the potential for large-scale, temporally precise monitoring and mapping of the cortex, without the use of invasive penetrating electrodes.