Spin qubits in semiconductor quantum dots are a very promising scalable qubit implementations but there are some challenges for further progress in this field: (i) Single-qubit manipulation requires highly localized oscillating magnetic fields, which are very hard to realize in practice; (ii) Hyperfine interaction between the electron spins in the quantum dots and the nuclear spins in the host semiconductor cause spin relaxation and dephasing; (iii) Another important source of dephasing is the charge noise in the gates that control the qubit. We propose a feasible and scalable quantum-dot-based implementation of a singlet-only spin qubit which is to leading order intrinsically insensitive to random effective magnetic fields set up by fluctuating nuclear spins in the host semiconductor. We show how the resulting qubit could be initialized, manipulated, and read out by electrical means only---without the need for magnetic fields---in a region of the parameter space where it is also insensitive to charge noise. Due to the intrinsic elimination of the effective nuclear fields and the charge noise from the qubit Hamiltonian, we find an improvement of the dephasing time of several orders of magnitude as compared to similar existing spin qubits.