The　experimental　studies　and　theoretical　analysis　of　the　effect　of　glass　barriers　on　AC　breakdown　characteristics　of　sphere-plane　gaps　are　presented.　Barriers　made　of　three　different　glass　materials　were　initially　tested　at　different　positions　in　a　fixed　sphere-plane　gap.　Then　silicate　glass　barriers　of　various　sizes　were　selected　for　further　tests　in　different　electrode　arrangements,　where　the　radius　of　the　sphere　varied　between　0.5　cm　and　2　cm　and　the　gap　distance　ranged　from　2　cm　to　5　cm　while　the　distance　from　the　barrier　surface　to　the　sphere　tip　was　fixed.　The　obtained　results　indicated　that　the　barrier　effect　was　most　significant　in　the　arrangement　with　the　smallest　radius　of　sphere　electrode,　longest　gap　distance　and　barriers　of　large　sizes　and　led　to　an　increase　of　breakdown　voltages.　The　highest　voltages,　up　to　205%　of　that　of　pure　air　gap,　were　obtained　for　configurations　providing　small　field　utilizations　factors,　which　were　evaluated　from　the　results　of　electric　field　calculations.　The　relationship　between　the　breakdown　voltage　levels　and　the　discharge　breakdown　paths　is　discussed.