[Author] Ustinov, Nikita S. [Title] On solvability of a critical semilinear problem with the spectral Neumann fractional Laplacian [AMS Subj-class] 35R11 Fractional partial differential equations 35A01 Existence problems for PDEs: global existence, local existence, non-existence [Abstract] We provide the sufficient conditions for the existence of the ground state solution for the problem generated by the fractional Sobolev inequality in $\Omega \in C^1:$ $(-\Delta)_{Sp}^s u(x) + u(x) = u^{2^*_s-1}(x)$. Here $(-\Delta)_{Sp}^s$ stands for the $s$-th power of the conventional Neumann Laplacian in $\Omega \Subset \mathbb{R}^n$, $n \geq 3$, $s \in (0, 1)$, $2^*_{s} = 2n/(n-2s)$. For the local case $s = 1$ corresponding results were obtained earlier for the Neumann Laplacian and Neumann $p$-Laplacian operators. [Comments] LaTeX, Russian, 15 pp. [Contact e-mail] ustinns@yandex.ru