CreateFrame - frameType: GameTooltip

[Platine]

What's wrong with the code below?

CreateFrame("GameTooltip", "ST_Tooltip", UIParent, "GameTooltipTemplate");
ST_Tooltip:ClearAllPoints();
ST_Tooltip:SetPoint("CENTER", UIParent, "CENTER", 0, 0);
ST_Tooltip:ClearLines();
ST_Tooltip:AddLine("My frame", 1, 1, 1);
ST_Tooltip:AddLine("Second line", 1, 1, 1);
ST_Tooltip:Show();

I cannot see my frame on the screen.