Triumphant exclamation upright character ignored in US state (3)
I believe the answer is:
oho
'triumphant exclamation' is the definition.
(I've seen this in another clue)
'upright character ignored in us state' is the wordplay.
'upright character' becomes 'I' (vertical letter of the alphabet).
'ignored in' indicates named letters should be taken away.
'us state' becomes 'ohio' (I've seen this before).
'ohio' with 'i' taken out is 'OHO'.
(Other definitions for oho that I've seen before include "Expression of surprise" , "Triumphant cry" , "I see!" .)