Spin qubits are widely studied as a candidate platform for building a quantum processor.Milestones in the field include reliable device fabrication, tuning and operation of spin qubits in one- and two-dimensional arrays. This thesis presents the results of experiments performed towards these objectives by fabricating, measuring, and manipulating twodimensional spin-qubit arrays encoded in electrostatically defined quantum dots. First, we present simulations of the charge stability diagram of a triple and a quadruple quantum dot, based on the matrix generalization of the constant interaction model. In particular, we focus on the three-dimensional visualization of the charge stability diagram of triple quantum dots and discuss its evolution for different spatial dots arrangements. Second, we review a series of advanced lithographical fabrication techniques required to fabricate the two-dimensional quantum dot arrays used for the spin-qubit experiment later presented. Next, we present our main experimental results obtained using singlet-triplet qubits in GaAs double quantum dots. We begin by reviewing several techniques for using single and double quantum dots as highly sensitive local probes for the calibration of the experimental setup. We then present two experimental techniques that allow us to verify the delay between two RF-channels at cryogenic temperatures. One technique is based on transport measurements of the charge pumped through a double quantum dot via the application of sinusoidal waveforms. The second technique uses two singlet-triplet qubits to measure the synchronization between two exchange control operations with sub-nanosecond resolution. Finally, we present further experiments on multiple spin qubit manipulation. In the first experiment, we demonstrate the simultaneous control of four singlet-triplet qubits by performing simultaneous exchange-controlled operations and T∗ 2 measurements across the array. In the final experiment, we investigate the possibility of coupling the qubits with a multielectron dot embedded in our device architecture, used as a quantum mediator. In particular, we show that we can bias the device in a configuration in which one of the qubits can be coherently coupled with the quantum mediator.