The TV favourite uploaded a video to Instagram of herself and fellow judge David Walliams dancing around in the ad break.
The comedian could be seen cutting some shapes to Rihanna’s hit song, We Found Love, playing in the background.
The camera then panned to Amanda jumping up and down moving her arms around in front of the lively crowd.
Behind the star, audience members could be seen with their hands up in the air, also jumping to the beat of the music.
Amanda wrote on the hilarious video: “If you’ve ever wondered what we get up to during the ads.”
The star looked incredible in a striking gown on the night, which boasted a thigh-slit design.
Amanda exposed her legs in the stunning number, as well as her cleavage, thanks to the daring cut.
The beauty uploaded images of her outfit to her Instagram, which received plenty of compliments from her 1.1 million followers.
Amanda uploaded a close-up shot of her dress alongside the caption: “Tonight’s look by my amazing team Hair: @itsdash Makeup: @karindarnell Stylist: @karl_willett Assistant: @adelepentland Gown: @jenniferclairofficial Shoes: @gianvitorossi Jewellery: @aspreylondon.”
One fan praised: “Wonderful wonderful wonderful.”
“You look stunning, love this colour on you,” gushed another.
A third added: “Looking super tonight as always.”
During tonight’s second live semi-final, magician act 4MG were voted through to the final by the public.
The judges, Amanda, David, Alesha Dixon and Simon Cowell, ended up voting comedy singer Siobhan Phillips through to the next round.
The acts will be joining police dog and handler, Dave and Finn, plus Flakefleet Primary School in Sunday’s final.
One previous act, Stavros Flatley, made a very surprising appearance on tonight’s show.
The duo, who were on the programme back in 2009, were on stage during 4MG’s magic routine.
Britain’s Got Talent third semi-final airs tomorrow on ITV from 7.30pm.