In general, semi-formal attire is defined as clothing that is more dressy than everyday or business attire, but not so formal as to include tuxedos or fancy gowns.
Semi-formal dress is still considered formal wear, however, and should be approached with this in mind. What type of clothing is appropriate for a semi-formal event also often depends on the event itself; semi-formal attire for a daytime wedding can be different from that worn to an evening business event or a party. For men, semi-formal attire typically means a dark suit and tie, while for women, it can include a cocktail dress or dressy suit.
Cocktail dresses, including little black dresses are nice choices as semi formal attires for a banquet:
Versatile to many occasions, cocktail dresses can be well dressed as semi-formal apparels and formal dresses.