Magnetic seizure therapy (MST) is under development as a means of improving cognitive outcomes with convulsive therapy through achieving better control over therapeutic seizure induction than is possible with conventional electroconvulsive therapy. In this investigation, we present the first neurophysiological characterization of high-dose MST (HD-MST, 6× seizure threshold) to see if a higher dose that is often used in human trials retains differential expression relative to electroconvulsive shock (ECS) and to explore the relationship between seizure expression and cognitive outcomes. To this end, rhesus monkeys received 4 weeks of daily treatment with ECS, HD-MST, and anesthesia-alone sham in counterbalanced order, with an interposed recovery period. Two channels of electroencephalogram were recorded during and immediately after the ictal period. Electroencephalogram power within delta, theta, alpha, and beta frequency bands was calculated. Electroconvulsive shock showed significantly more ictal power in all frequency bands than HD-MST (P < 0.01). Electroencephalogram power during the postictal period was significantly different among conditions only for the delta band. Higher ictal expression with ECS was associated with slowed completion time for an orientation task given immediately after the treatments. Our results support earlier findings demonstrating that MST- and ECS-induced seizures elicit differential patterns of ictal expression, consistent with the relatively more superficial stimulation achieved via magnetic induction in comparison with conventional electroconvulsive therapy. These results demonstrate that MST, even at high dose, results in seizures that differ neurophysiologically from ECS. It further suggests that some of the differences in ictal expression may relate to the improved cognitive outcomes seen with MST.