Sofia Vergara‘s keeping her clothing casual while enjoying a chill Fourth of July weekend … letting everyone see her impressive backside while tanning.

The actress shared a vid from her vacation in Ibiza in honor International Bikini Day on Saturday … in which she’s lying on her front in a thong-style bikini — meaning no coverage at all on her booty.

Like we said, she’s lying on her front so we can’t see her bikini top — but, the strings in back don’t seem to be tied … so, it seems safe to assume she’s letting it all hang out.

Sofia’s no stranger to European vacations obviously … just recently going to France with Heidi Klum — her “America’s Got Talent” co-judge who is also know for stripping down.