Despite recent advances in bioinspired underwater adhesives, achieving tough, fast, and stable adhesion in aqueous environments is still challenging. Here, an underwater super-tape with semi-interpenetrating polymer networks (SIPNs) and a water-repelling liquid surface is synthesized. In the SIPN, the linear chains easily diffuse to adapt to the adherends, and the cross-linked chains provide the super-tape with high dimensional stability. Meanwhile, both the linear and cross-linked chains bear many catechol groups, which can not only vigorously interact with the adherends but also form numerous hydrogen bonds serving as sacrificial bonds in the SIPN. Thus, the super-tape shows both high interfacial adhesion and cohesive energy. Moreover, the super-tape is covered with a water-repelling liquid surface by spraying it with traces of a hydrophobic solvent. It is demonstrated that the hydrophobic solvent absorbed on the surface of the super-tape can remove water between the tape and adherends, enabling their intimate contact to form a strong interaction. As such, the super-tape shows excellent instant adhesion property under water, and the adhesive strength and toughness increase with time and reach their maximum values at around 5 h. The maximum debonding energy of the super-tape reaches 3933 J m–2, which is much higher than those of existing double-sided tapes.