The behavior of the ionosphere in Russia’s Arctic region during periods of strong sudden stratospheric warmings was investigated using data from the international network of phase dual-frequency GPS/GLONASS receivers, global ionospheric maps (GIM) of the total electron content (TEC) and vertical sounding data. Six events of major stratospheric warmings that have occurred in the Northern hemisphere over the last decade were considered. In order to identify the possible response of the high-latitude ionosphere to SSW events, we carried out the analysis of the total electron content and F2-layer electron density deviation from the background level. Spatial and temporal distributions of the amplitude of diurnal TEC variations were also studied. The dynamics of the high-latitude ionosphere at the points near the SSW zone during the periods of warmings was found to differ from the regular. We also revealed that the events of major SSWs are usually accompanied by a decrease in amplitude of diurnal TEC variations during the SSW development stage and by an increase in amplitude, which may be observed at latitudes of up to ∼75◦ N after the SSW peak.