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The sentence is "correct" but it requires some explanations.
In order to derive the common equations regarding electronic devices (such as the I-V relation in a pn diode),you must suppose that the size of the device is a lot smaller than the operation wavelength: this is done to justify the use of a simplified electromagnetic model (just the Poisson equation) instead of a complex set of relations (Maxwell's equations) that would be very hard to manipulate.
Moreover, the common Kirchhoff equations are valid only if the wavelenght is longer than the size of the circuit.